Hi weedgrower, I am new to this site and to computers, I wouln't have got the far without a teenager in the house!
I am year two of my allotment, a student of horticulture, with over 80 books on the subject. I've consulted the RHS -propogating plants and as long as you propogate from healthy plants your good to go for another three years. Plants can also be divided in spring or you keep some aside for propogation only by removing the flowers and pegging down runners.
I'm glad you brought this up cos I needed to know myself, I bought some perpetual strawberries from J. Parkers had then in the greenhouse all winter now in coldframe. Will be interesting to compare with other varieties.